The prevalence of diabetes mellitus Type 2 could be significantly reduced by early identification of subjects at risk, allowing for better prevention and earlier treatment. Glucose intolerance (GI) is a hallmark of the prediabetic stage. This study aims at identifying 1) prognostic biomarkers predicting the risk of developing GI later in life and 2) diagnostic biomarkers reflecting the degree of already manifest GI. To this end, disease development was followed over time in mice, and biomarkers were identified using lipidomics and transcriptomics. Young adult ApoE3Leiden mice were treated a high-fat diet for 12 wk to induce GI. Blood was collected before and during disease development. The individual extent of GI was determined with a glucose tolerance test and the area under the curve (AUC) was calculated for each animal. Subject-specific AUC values were correlated to the plasma lipidome (t = 0) and the white blood cell (WBC) transcriptome (t = 0, 6, and 12 wk) to identify prognostic and diagnostic biomarkers, respectively. The plasma ratio of specific free fatty acids prior to high-fat feeding (C16:1/C16:0, C18:1/C18:0 and C18:2/C22:6) was significantly correlated with the AUC and predictive for future GI. Subsequently, the expression level of specific WBC genes (Acss2, Arfgap1, Tfrc, Cox6b2, Barhl2, Abcb4, Cyp4b1, Sars2, Fgf16, and Tceal8) reflected the individual degree of GI during disease progression. Specific plasma free fatty acids as well as their ratio can be used to predict future GI. The expression levels of specific WBC genes can serve as easy accessible markers to diagnose and monitor already existing GI.

Adamant progression of chronic cholangiopathies towards cirrhosis and limited therapeutic options leave a liver transplantation the only effective treatment. Insulin-like growth factor 1 (IGF1) effectively blocks fibrosis in acute models of liver damage in mice, and a phase I clinical trial suggested an improved liver function. IGF1 targets the biliary epithelium, but its potential benefit in chronic cholangiopathies has not been studied. To investigate the possible therapeutic effect of increased IGF1 expression, we crossed Abcb4(-/-) mice (a model for chronic cholangiopathy), with transgenic animals that overexpress IGF1. The effect on disease progression was studied in the resulting IGF1-overexpressing Abcb4(-/-) mice, and compared to that of Abcb4(-/-) littermates. The specificity of this effect was further studied in an acute model of fibrosis. The overexpression of IGF1 in transgenic Abcb4(-/-) mice resulted in stimulation of fibrogenic processes - as shown by increased expression of Tgfß, and collagens 1, 3 and 4, and confirmed by Sirius red staining and hydroxyproline measurements. Excessive extracellular matrix deposition was favored by raise in Timp1 and Timp2, while a reduction of tPA expression indicated lower tissue remodeling. These effects were accompanied by an increase in expression of inflammation markers like Tnfα, and higher presence of infiltrating macrophages. Finally, increased number of Ck19-expressing cells indicated proliferation of biliary epithelium. In contrast to liver fibrosis associated with hepatocellular damage, IGF1 overexpression does not inhibit liver fibrogenesis in chronic cholangiopathy.

Chemotherapy failure remains a challenge when treating patients with acute myeloid leukemia (AML), who often suffer from persistent or relapsed disease. The multidrug resistance (MDR) mediated by efflux transporters of the ATP binding cassette (ABC) superfamily is a major obstacle for successful chemotherapy. The present study aimed to elucidate whether the expression of ABC transporters was associated with prognostic factors and responses to chemotherapy in patients with AML, with particular focus on whether co-expression of multiple ABC transporters resulted in a worse prognosis. In the present study, the mRNA expression levels of ABC transporters ABCB1, ABCB4, ABCC1, ABCC4 and ABCG2 in bone marrow (BM) mononuclear cell (MNC) samples from 96 de novo patients with AML and in the peripheral blood (PB) MNC samples from 22 normal individuals were investigated using reverse transcription-quantitative polymerase chain reaction analysis. It was revealed that ABCB1, ABCC1, ABCC4 and ABCG2 were expressed at higher levels in patients with AML compared with normal individuals, whereas ABCB4 had a lower expression level. The expression of ABCB4 in patients with AML was significantly lower than in normal individuals (P<0.001). Patients risk status was associated with ABCB1 (P=0.037), ABCC1 (P=0.047), ABCC4 (P=0.015) and ABCG2 (P=0.027). The 4 genes were expressed a significantly higher levels in the poor response group compared with the good response group (ABCB1, P=0.014; ABCC1, P=0.021; ABCC4, P=0.005; ABCG2, P=0.009). The overexpression of the 4 ABC transporters and the complete remission rate were inversely correlated (P<0.001). These results suggest that the co-expression of multiple ABC transporters may contribute to a worse prognosis in AML.

BACKGROUND

Ursodeoxycholic acid (UDCA) therapy is commonly used in intrahepatic cholestasis of pregnancy (ICP).

OBJECTIVE

To evaluate the efficacy and tolerance of UDCA in real-world conditions and to search for factors predictive of response to treatment.

METHODS

This observational study included 98 consecutive patients suffering from pruritus during pregnancy associated with increased ALT levels or total bile acid (TBA) concentrations, without other causes of cholestasis. The entire ABCB4 gene coding sequence was analyzed by DNA sequencing.

RESULTS

UDCA was prescribed until delivery in all patients (mean dose 14.0mg/kg/day; mean duration 30.4 days). Pruritus improved in 75/98 (76.5%) patients, and totally disappeared before delivery in 25/98 (25.5%). After 2-3 weeks of treatment, ALT levels decreased by more than 50% of base line in 67/86 (77.9%) patients and normalized in 34/86 (39.5%), and TBA concentrations decreased in 28/81 (34.6%). Only one patient stopped the treatment before delivery. On multivariate analysis, ALT >175IU/l before treatment was associated with improvement of pruritus (OR 2.97, 95% CI 1.12-7.89, P=0.029) and with decreased ALT (OR 18.61, 95% CI 3.94-87.99, P=0.0002). ABCB4 gene mutation was not associated with response to treatment.

CONCLUSIONS

This study supports the use of UDCA as first line therapy in ICP.

OBJECTIVE

Single gene mutations cause syndromes of intrahepatic cholestasis, but previous multi-gene mutation screening in children with idiopathic cholestasis failed to fulfill diagnostic criteria in approximately two-thirds of children. In adults with fibrosing cholestatic disease, heterozygous ABCB4 mutations were present in 34% of patients. Here, we hypothesized that children with idiopathic cholestasis have a higher frequency of heterozygous non-synonymous gene sequence variants.

METHODS

We analyzed the frequency and types of variants in 717 children in whom high-throughput sequencing of the genes SERPINA1, JAG1, ATP8B1, ABCB11 and ABCB4 was performed as part of an evaluation for idiopathic intrahepatic cholestasis cholestasis. The frequency of non-synonymous variants (NSV) was compared with those of 1092 control subjects enrolled in the 1000 Genome Project.

RESULTS

The frequency of NSV in single genes was similar between disease (25%) and controls (26%, P = 0.518). In contrast, double or triple NSV in two or more genes were more frequent in disease (n = 7%) than controls (n = 4.7%, P = 0.028). Detailed review of clinical and laboratory information in a subgroup of double or triple heterozygous patients revealed variable γ-glutamyltransferase levels and severity of pruritus, with liver biopsies showing stage 2-3 fibrosis.

CONCLUSIONS

Children with idiopathic intrahepatic cholestasis have a higher frequency of double or triple NSV in SERPINA1, JAG1, ATPB1, ABCB11 or ABCB4. These findings raise the potential role for gene-gene relationships in determining the phenotype of cholestatic liver disease in children.

ATP Binding Cassette Transporter A4 (ABCB4) is a sterol export pump that regulates excretion of biliary cholesterol. We tested association between ABCB4 polymorphisms and gallstone disease using meta-analysis. In a cross-sectional study, 296 subjects were recruited from a hospital-based population. Total of 171 subjects were diagnosed as gallstone disease by abdominal ultrasonography from three cohort studies. We evaluated prevalence of ABCG8 rs11887534 (D19H) as a positive control, and the ABCB4 rs1202283 and rs2230028 polymorphisms on Chinese population were screened by meta-analysis and genotyped using TaqMan® SNP assay. Stata/SE 11.0 software and random-effects model were used in meta-analyzing 3 cohort between study heterogeneity. Four studies including three cohorts were used for final meta-analysis. In allelic model, minor alleles of ABCB4 rs1202283 (OR = 0.41, 95% CI: 0.25-0.67, P<0.001) and of ABCB4 rs2230028 (OR = 0.12, 95% CI: 0.06-0.22, P = 0.001) were associated with an increased risk for gallstone disease in Europeans. Funnel plot and Egger's test suggested absence of publication bias. Concentration of total cholesterol, low-density lipoprotein cholesterol (LDLC) (P = 0.015) and high-density lipoprotein cholesterol (HDLC) (P = 0.028) were significantly higher in subjects with gallstones disease than controls. ABCB4 rs1202283 (heterozygote AG) (P<0.0001), rs2230028 (heterozygote CT) (P = 0.023) and ABCG8 rs11887534 (heterozygote CG) (P = 0.006) were significantly associated with gallstone disease in Chinese population. Genetic risk associated with ABCB4 rs2230028 (homozygote GG) polymorphism was dominated in asymptomatic gallstone disease (95% C.I.: 0.219-0.768; P = 0.005). In conclusion, carriers of ABCB4 rs1202283, rs2230028 are at an increased risk for gallstone disease, while ABCB4 rs2230028 is associated with asymptomatic gallstone disease.

The ATP-binding cassette half-transporters Abcg5 and Abcg8 promote the secretion of neutral sterols into bile. Studies have demonstrated the diet-induced expression of these transporters in liver, but precisely where this occurs remains to be elucidated. This study investigated the changes in the expression of these transporters in bile canaliculi in cholesterol-loaded livers. Mice were fed either a standard (SD) diet or a high-fat and high-sucrose (HF/HS) diet for 3 weeks. Bile canaliculi proteins and cryosections were prepared from the liver, and the protein levels and distribution of Abcg5/Abcg8 were determined. The high-calorie diet induced a marked accumulation of lipids in mouse liver. Protein levels of Abcg5 and Abcg8 in bile canaliculi were significantly increased by the HF/HS diet compared to the SD diet. No significant differences in Abca1, Abcb4 (Mdr2), Abcb11 (Bsep), or Abcc2 (Mrp2) levels were observed. Immunohistochemical analyses confirmed that these increases occurred in bile canaliculi. These results suggest that diet-induced lipid loading of the liver causes a significant increase in the expression of Abcg5 and Abcg8 in bile canaliculi.

OBJECTIVE

Doxorubicin is one of the most active agents in the first-line therapy for metastatic breast cancer, but its utility is partially limited by the frequent emergence of doxorubicin resistance. In this study, we aimed to investigate the role of ATP-binding cassette sub-family B, member 4 (ABCB4) in acquired doxorubicin resistance in breast cancer cells, as well as its potential mechanism.

METHODS

In doxorubicin-sensitive and -resistant breast cancer cell lines MCF-7 and MDA-MB-231, the expression levels of ABCB4 were detected using real-time quantitative PCR and Western blot analysis, the DNA methylation and histone acetylation status of ABCB4 gene were investigated by bisulfite-sequencing PCR (BSP) and chromatin immunoprecipitation (ChIP) assays, and the doxorubicin sensitivity and intracellular doxorubicin accumulation were observed using cell cytotoxicity assay and flow cytometry. In Madin-Darby Canine Kidney (MDCKII) cells, In vitro transport assay was used to assess the ABCB4-mediated transport of doxorubicin.

RESULTS

ABCB4 was overexpressed in doxorubicin-resistant breast cancer cells compared to their doxorubicin-sensitive counterparts, which was associated with reduced DNA methylation as well as increased histone acetylation at the ABCB4 promoter. ABCB4 could actively pump doxorubicin out of the cells, and knockdown of ABCB4 increased doxorubicin sensitivity and intracellular accumulation in doxorubicin-resistant breast cancer cells.

CONCLUSIONS

Our results indicate that ABCB4 is overexpressed in breast cancer cells with acquired doxorubicin resistance, which could be attributed, at least partially, to the epigenetic modifications of ABCB4 gene. ABCB4 mediates the efflux transport of doxorubicin, and contributes to the acquired resistance of doxorubicin in breast cancer cells.

The ABCB4 gene codes for a protein involved in the transport of phosphatidylcholine across the canalicular membrane of the hepatocyte. ABCB4 gene defects have been associated with progressive familial intrahepatic cholestasis type 3, intrahepatic cholestasis of pregnancy, adult biliary cirrhosis and the more recently described low phospholipid associated cholelithiasis syndrome. The present paper describes 2 probands with a long history of recurrent pancreatitis and cholelithiasis and the same heterozygous, as yet undescribed del 3683>3688 within exon 28 of the ABCB4 gene resulting in a loss of function. This report shows that ABCB4 mutations may cause acute recurrent biliary pancreatitis.

ABCB4 (MDR3), a lipid translocator, moves phosphatidylcholine from the inner to the outer leaflet of the canalicular membrane. Genetic mutations of ABCB4 lead to three distinct but related hepatobiliary diseases. Progressive familial intrahepatic cholestasis (PFIC) type 3 is a chronic cholestatic syndrome characterized by a markedly elevated gamma-glutamyltranspeptidase. Patients present with jaundice, pruritus, and hepatosplenomegaly. Periportal inflammation progresses to biliary cirrhosis and causes portal hypertension. Ursodeoxycholic acid (UDCA) normalizes liver function tests in approximately one half of treated PFIC type 3 patients. Partial responders or nonresponders eventually will require liver transplantation. Gallstone patients with ABCB4 mutations may have low phospholipid-associated cholelithiasis syndrome, characterized by cholesterol gallstones and intrahepatic microlithiasis, along with recurrent biliary symptoms, despite cholecystectomy. Patients with ABCB4 mutations also may develop intrahepatic brown pigment stones. UDCA may improve biliary symptoms even before the dissolution of stones occurs. Additional therapies such as farnesoid X receptor ligands/agonists and benzfibrates show future therapeutic promise. Intrahepatic cholestasis of pregnancy affects pregnant women with abnormal ABCB4. These women suffer from disabling pruritus and also may experience steatorrhea. Fetuses are at high risk for prematurity and stillbirths. The definitive treatment is delivery of the baby. In the interim, limited fat intake, fat-soluble vitamin supplementation, and UDCA with or without S-adenosylmethionine can provide symptomatic relief. Additional hepatobiliary diseases related to ABCB4 mutations are likely to be identified. This may result in the discovery of additional therapies for PFIC type 3, gallstones, and intrahepatic cholestasis of pregnancy.

ABCB4, which is specifically expressed on the canalicular membrane of hepatocytes, exports phosphatidylcholine (PC) into bile. Because SM depletion increases cellular PC content and stimulates PC and cholesterol efflux by ABCA1, a key transporter involved in generation of HDL, we predicted that SM depletion also stimulates PC efflux through ABCB4. To test this prediction, we compared the lipid efflux activity of ABCB4 and ABCA1 under SM depletion induced by two different types of inhibitors for SM synthesis, myriocin and (1R,3S)-N-(3-hydroxy-1-hydroxymethyl-3-phenylpropyl)dodecanamide, in human embryonic kidney 293 and baby hamster kidney cells. Unexpectedly, SM depletion exerted opposite effects on ABCB4 and ABCA1, suppressing PC efflux through ABCB4 while stimulating efflux through ABCA1. Both ABCB4 and ABCA1 were recovered from Triton-X-100-soluble membranes, but ABCB4 was mainly recovered from CHAPS-insoluble SM-rich membranes, whereas ABCA1 was recovered from CHAPS-soluble membranes. These results suggest that a SM-rich membrane environment is required for ABCB4 to function. ABCB4 must have evolved to exert its maximum activity in the SM-rich membrane environment of the canalicular membrane, where it transports PC as the physiological substrate.

ABCB4/MDR3, a member of the ABC superfamily, is an ATP-dependent phosphatidylcholine translocator expressed at the canalicular membrane of hepatocytes. Defects in the ABCB4 gene are associated with rare biliary diseases. It is essential to understand the mechanisms of its canalicular membrane expression in particular for the development of new therapies. The stability of several ABC transporters is regulated through their binding to PDZ (PSD95/DglA/ZO-1) domain-containing proteins. ABCB4 protein ends by the sequence glutamine-asparagine-leucine (QNL), which shows some similarity to PDZ-binding motifs. The aim of our study was to assess the potential role of the QNL motif on the surface expression of ABCB4 and to determine if PDZ domain-containing proteins are involved. We found that truncation of the QNL motif decreased the stability of ABCB4 in HepG2-transfected cells. The deleted mutant ABCB4-ΔQNL also displayed accelerated endocytosis. EBP50, a PDZ protein highly expressed in the liver, strongly colocalized and coimmunoprecipitated with ABCB4, and this interaction required the QNL motif. Down-regulation of EBP50 by siRNA or by expression of an EBP50 dominant-negative mutant caused a significant decrease in the level of ABCB4 protein expression, and in the amount of ABCB4 localized at the canalicular membrane. Interaction of ABCB4 with EBP50 through its PDZ-like motif plays a critical role in the regulation of ABCB4 expression and stability at the canalicular plasma membrane.

Adenosine triphosphate binding cassette transporter, subfamily B member 4 (ABCB4) is the transporter of phosphatidylcholine at the canalicular membrane of hepatocytes. ABCB4 deficiency, due to genetic variations, is responsible for progressive familial intrahepatic cholestasis type 3 (PFIC3) and other rare biliary diseases. Roscovitine is a molecule in clinical trial that was shown to correct the F508del variant of cystic fibrosis transmembrane conductance regulator (CFTR), another ABC transporter. In the present study, we hypothesized that roscovitine could act as a corrector of ABCB4 traffic-defective variants. Using HEK and HepG2 cells, we showed that roscovitine corrected the traffic and localisation at the plasma membrane of ABCB4-I541F, a prototypical intracellularly retained variant. However, roscovitine caused cytotoxicity, which urged us to synthesize non-toxic structural analogues. Roscovitine analogues were able to correct the intracellular traffic of ABCB4-I541F in HepG2 cells. Importantly, the phospholipid secretion activity of this variant was substantially rescued by three analogues (MRT2-235, MRT2-237 and MRT2-243) in HEK cells. We showed that these analogues also triggered the rescue of intracellular traffic and function of two other intracellularly retained ABCB4 variants, i.e. I490T and L556R. Our results indicate that structural analogues of roscovitine can rescue genetic variations altering the intracellular traffic of ABCB4 and should be considered as therapeutic means for severe biliary diseases caused by this class of variations.

OBJECTIVE

The lysyl oxidase-like protein 2 (LOXL2) promotes stabilization of the extracellular matrix, chemotaxis, cell growth and cell mobility. We aimed to (i) identify stimuli of LOXL2 in cholangiopathies, (ii) characterize the effects of LOXL2 on biliary epithelial cells' (BECs) barrier function, (iii) compare LOXL2 expression in primary sclerosing cholangitis (PSC), primary biliary cholangitis, and disease controls, and (iv) to determine LOXL2 expression and its cellular sources in four mouse models of cholangiopathies.

METHODS

Cultured murine BECs were challenged with well-known triggers of cellular senescence, hypoxia, phospholipid-deficient Abcb4-/- mouse bile and chenodeoxycholic acid and investigated for LOXL2, SNAIL1 and E-cadherin expression and transepithelial electrical resistance with and without LOX-inhibition. In vivo, LOXL2 expression was studied in PSC livers, and controls and mouse models. We compared LOXL2 serum levels in patients with PSC, secondary SC, primary biliary cholangitis, and controls.

RESULTS

Cellular senescence, hypoxia, Abcb4-/- bile and chenodeoxycholic acid induced LOXL2 and SNAIL1 expression, repressed E-cadherin expression, and significantly reduced transepithelial electrical resistance in BECs. Notably, all of the pathological changes could be recovered via pharmacological LOX-inhibition. Mouse models showed induced LOXL2 expression in the portal region and in association with ductular reaction. LOXL2 serum levels were significantly elevated in patients with cholangiopathies. In PSC, LOXL2 expression was located to characteristic periductal onion skin-type fibrosis, ductular reaction, Kupffer cells, and fibrotic septa. Importantly, in PSC, LOXL2 overexpression was paralleled by E-cadherin loss in BECs from medium-sized bile ducts.

CONCLUSIONS

Reactive BECs produce LOXL2, resulting in increased tight junction permeability, which can be ameliorated by pharmacological LOX-inhibition in vitro. Reactive BECs, portal myofibroblasts, and Kupffer cells are the main sources of LOXL2 in cholangiopathies.

UNASSIGNED

In this study, we investigate the role of lysyl oxidase-like protein 2 (LOXL2), an enzyme pivotal in the development of organ fibrosis, in the pathogenesis of cholangiopathies (diseases of bile ducts), such as primary sclerosing cholangitis. We found LOXL2 to be expressed in association with bile duct epithelial injury and uncovered mechanisms for its upregulation and the subsequent effects in vitro and in vivo. Our findings support testing of anti-LOXL2 treatment strategies for patients with primary sclerosing cholangitis.

ATP binding cassette (ABC) transporter proteins include efflux pumps that confer multixenobiotic resistance to zebrafish embryos, a valuable toxico/pharmacological model. Here, we established an automated microscopy-based rhodamine B dye accumulation assay in which enhanced dye accumulation in live zebrafish embryos indicates inhibition of multixenobiotic efflux transporter activity. Twenty structurally divergent known substrates and/or inhibitors of human ABC transporters and environmentally relevant compounds were examined using this assay and the ATPase activity of recombinant zebrafish Abcb4 as readouts. These two assays confirmed that Abcb4 functions as an efflux transporter in zebrafish, whereas they gave discordant results for some of the tested substances. The dye accumulation assay in zebrafish embryos could be useful to screen environmental pollutants and other chemicals for efflux transporter interaction in a medium-throughput fashion.

Keywords: ABC efflux transporter; ATPase activity; chemosensitizer; dye accumulation assay; recombinant protein; zebrafish Abcb4; zebrafish embryo.

Accumulation of bile salts (BSs) during cholestasis leads to hepatic and biliary injury, driving inflammatory and fibrotic processes. The Na+ -Taurocholate Cotransporting Polypeptide (NTCP) is the major hepatic uptake transporter of BSs, and can be specifically inhibited by myrcludex B. We hypothesized that inhibition of NTCP dampens cholestatic liver injury. Acute cholestasis was induced in mice by a 3.5-diethoxycarbonyl-1.4-dihydrocollidine (DDC) diet or by bile duct ligation (BDL). Chronic cholestasis was investigated in Atp8b1-G308V and Abcb4/Mdr2 deficient mice. Mice were injected daily with myrcludex B or vehicle. Myrcludex B reduced plasma alkaline phosphatase (ALP) levels in DDC-fed, Atp8b1-G308V and BDL mice by 39%, 27% and 48% respectively. Expression of genes involved in fibrosis, proliferation and inflammation was reduced by myrcludex B treatment in DDC-fed and Atp8b1-G308V mice. NTCP-inhibition increased plasma BS levels from 604±277 to 1746±719 μm in DDC-fed mice, 432±280 to 762±288 μm in Atp8b1-G308V mice and from 522±130 to 3625±378 μm in BDL mice. NTCP-inhibition strongly aggravated weight loss in BDL mice, but not in other cholestatic models studied. NTCP-inhibition reduced biliary BS output in DDC-fed and Atp8b1-G308V mice by ∼50% while phospholipid (PL) output was maintained, resulting in a higher PL/BS ratio. Conversely, liver injury in Abcb4 deficient mice, lacking biliary phospholipid output, was aggravated after myrcludex B treatment.

CONCLUSIONS

NTCP-inhibition by myrcludex B has hepatoprotective effects, by reducing BS load in hepatocytes and increasing the biliary PL/BS ratio. High micromolar plasma BS levels after NTCP-inhibition were well tolerated. NTCP-inhibition may be beneficial in selected forms of cholestasis. (Hepatology 2018).

Circadian regulation of hepatic detoxification seems to be amongst the key roles of the biological clock. The liver is the major site for biotransformation, and in mammals, it contains several clock-controlled transcription factors such as proline and acidic amino acid-rich basic leucine zipper proteins (PAR bZIP) and basic-helix-loop-helix Per-Arnt-Sim (bHLH-PAS) family that act as circadian regulators of detoxification genes. This investigation explored the existence of daily and circadian expression of transcription factors involved in detoxification, as well as the temporal profile of a set of their target genes in zebrafish liver. In our study, zebrafish were able to synchronize to a light-dark (LD) cycle and displayed a diurnal pattern of activity. In addition, the expression of clock genes presented daily and circadian rhythmicity in liver. Apart from hlfa, the expression of PAR bZIP transcription factors also displayed daily rhythms, which appeared to be both light-dependent and clock-controlled, as circadian rhythms free-ran under constant conditions (continuous darkness, DD). Under LD, tefb, dbpa and dbpb expression peaked at the end of the darkness period whereas tefa showed peak levels of expression at the onset of the photophase. In addition, these four genes exhibited circadian expression under DD, with higher expression levels at the end of the subjective night. The expression of the bHLH-PAS transcription factor arh2 also showed circadian rhythmicity in zebrafish liver, peaking in the middle of the subjective night and approximately 3-4 h before peak expression of the PAR bZIP genes. Regarding the detoxification genes, the major target gene of AhR, cyp1a, showed daily and circadian expression with an acrophase 2 h after ahr2. Under LD, abcb4 also showed daily rhythmicity, with an acrophase 1-2 h after that of PAR bZIP factors during the transition between darkness and light phases, when zebrafish become active. However, the expression of six detoxification genes showed circadian rhythmicity under DD, including cyp1a and abcb4 as well as gstr1, mgst3a, abcg2 and sult2_st2. In all cases, the acrophases of these genes were found during the second half of the subjective night, in phase with the PAR bZIP transcription factors. This suggested that their expression is clock-controlled, either directly by core clock genes or through transcription factors. This study presents new data demonstrating that the process of detoxification is under circadian control in fish. Results showed that time of day should be considered when designing toxicological studies or administering drugs to fish.

Background & aim: ABCB4 is expressed at the canalicular membrane of hepatocytes. This ATP-binding cassette (ABC) transporter is responsible for the secretion of phosphatidylcholine into bile canaliculi. Missense genetic variations of ABCB4 are correlated with several rare cholestatic liver diseases, the most severe being progressive familial intrahepatic cholestasis type 3 (PFIC3). In a repurposing strategy to correct intracellularly retained ABCB4 variants, we tested 16 compounds previously validated as cystic fibrosis transmembrane conductance regulator (CFTR) correctors.

Methods: The maturation, intracellular localization and activity of intracellularly retained ABCB4 variants were analyzed in cell models after treatment with CFTR correctors. In addition, in silico molecular docking calculations were performed to test the potential interaction of CFTR correctors with ABCB4.

Results: We observed that the correctors C10, C13 and C17, as well as the combinations of C3+C18 and C4+C18, allowed the rescue of maturation and canalicular localization of four distinct traffic-defective ABCB4 variants. However, such treatments did not permit a rescue of the phosphatidylcholine secretion activity of these defective variants and were also inhibitory of the activity of wild type ABCB4. In silico molecular docking analyses suggest that these CFTR correctors might directly interact with transmembrane domains and/or ATP-binding sites of the transporter.

Conclusion: Our results illustrate the uncoupling between the traffic and the activity of ABCB4 since the same molecules can rescue the traffic of defective variants while they inhibit the secretion activity of the transporter. We expect that this study will help to design new pharmacological tools with potential clinical interest.

Keywords: ABC transporters; Bile secretion; Cell models; Cholestatic liver diseases; Molecular docking; Targeted pharmacotherapy.

MDR3 is a hepatocyte canalicular membrane protein encoded by the ABCB4 gene located on chromosome 7. MDR3 mediates the translocation of phosphatidylcholine into bile. Severe MDR 3 deficiency typically presents during early childhood with chronic cholestasis evolving to cirrhosis and portal hypertension, requiring liver transplantation. Herein, we report a case of severe MDR3 deficiency in a male child diagnosed with negative MDR3 immunostaining in hepatic canaliculi who underwent LDLT at our centre. We also describe single incidentally detected early well-differentiated HCC in the explant liver. The patient is on regular follow-up and is doing well. Our report shows that MDR3 deficiency may be a risk factor for the development of HCC.

The ATP binding cassette subfamily B member 4 (ABCB4) gene on chromosome 7 encodes the ABCB4 protein (alias multi drug resistance 3 protein [MDR3]), a P-glycoprotein in the canalicular membrane of the hepatocytes that acts as a translocator of phospholipids into bile. Several variants in ABCB4 have been identified so far that lead to ABCB4 deficiency accounting for a disease spectrum ranging from progressive familial cholestasis type 3 (PFIC-3) to less severe forms presenting as low phospholipid associated cholelithiasis (LPAC), intrahepatic cholestasis of pregnancy (ICP) or drug-induced liver injury (DILI). Furthermore, whole genome sequencing identified ABCB4 variants to be associated with an increased incidence of gallstone disease, gallbladder and cholangiocarcinoma, liver cirrhosis or elevated liver function tests. Diagnosis of ABCB4 deficiency related diseases is based on clinical presentation, serum biomarkers, imaging techniques, liver histology and genetic testing. Nevertheless, the clinical presentation can vary widely and clear genotype-phenotype correlations are lacking so far. Ursodeoxycholic acid is the most commonly used medical treatment, but confirmation of its benefit by large controlled clinical studies is still lacking. Future pharmacological options may include stimulation/restoration of residual function by chaperones (e.g. 4-phenyl butyric acid, curcumin) or induction of ABCB4 transcription by farnesoid X receptor (FXR) agonists or PPARα-ligands/fibrates. In cirrhotic patients with end stage liver disease or patients with intractable pruritus orthotopic liver transplantation remains the last and often only therapeutic option.

Nonalcoholic steatohepatitis (NASH) is an emerging health crisis with no approved therapies. Obeticholic acid (OCA), a farnesoid X receptor (FXR) agonist, shows promise in NASH trials. However, the precise mechanisms mediating OCA effects and impact on cholesterol metabolism are not fully understood. We explored the pharmaco-toxicological effects of OCA on patho-physiological pathways in hepatocytes using a previously described perfused organotypic liver system that allows culture in near-physiological insulin/glucose milieus, and exhibits drug responses at clinically-relevant concentrations. Primary hepatocytes experienced 48-hour exposure to OCA at concentrations approximating therapeutic (0.5μM) and supratherapeutic (10μM) levels. Global transcriptomics by RNAseq was complimented by cellular viability (MTT), CYP activity assays, and secreted FGF19 levels in the media. Dose-dependent, transcriptional effects suggested suppression of bile acid synthesis (↓CYP7A1, ↓CYP27A1) and increased bile efflux (↑ABCB4, ↑ABCB11, ↑OSTA, ↑OSTB). Pleiotropic effects included suppression of TGFβ and IL-6 signaling pathways, and signatures suggestive of HDL suppression (↑SCARB1, ↓ApoAI, ↓LCAT) and LDL elevation (↑ApoB, ↓CYP7A1). OCA exhibited direct FXR-mediated effects with increased FGF19 secretion. Transcriptomics revealed regulation of metabolic, anti-inflammatory, and anti-fibrotic pathways beneficial in NASH, and predicted cholesterol profiles consistent with clinical findings. Follow-up studies under lipotoxic/inflammatory conditions would corroborate these effects in a disease-relevant environment.